Synchronous messaging protocols, such as Motorola's FLEX.TM. protocol for a messaging system, require the periodic transmission of synchronization signals so that the wireless messaging units used in the messaging system can maintain synchronization with the system. The FLEX.TM. protocol, for example, requires a synchronization word at the beginning of each frame, i.e., every 1.875 seconds.
Some existing and proposed systems can encounter difficulties in providing sufficient synchronization signals to keep the wireless messaging units synchronized. Examples are: shared systems, high speed Quadrature Amplitude Modulation (QAM) systems, frequency-hopped spread-spectrum (FHSS) systems, and two-way systems. In a shared system, the synchronization signals of one system are interrupted when the other system uses the channel. In QAM systems, for best efficiency the designers prefer to use only a QAM sync, but a QAM sync is more difficult to acquire than a frequency-shift-keyed (FSK) sync. In a FHSS system, if synchronization is lost, the receiver will have great difficulty finding where in the frequency hopping sequence the transmitted signal is, and scanning will be lengthy. In a two-way system, the wireless messaging units' inbound transmissions are synchronized with the outbound transmissions. Maintaining synchronization between widely separated synchronization signals calls for expensive crystals in the wireless messaging units.
Thus, what is needed is a method and apparatus in a wireless messaging unit for establishing transmitter or receiver synchronization. Preferably, the method and apparatus will not add great expense to the wireless messaging unit.